The long-term goal of this research is to discover the force transmission and force transduction pathways responsible for touch and proprioception. These senses are essential for social communication and every aspect of daily life from sitting, to standing, to running; however, their function is disrupted in both inherited and acquired diseases, including HIV-AIDS and diabetes. Even partial loss of sensory function as in diabetic peripheral neuropathy (DPN) has devastating consequences; DPN affects an estimated 15 million Americans and is the dominant risk factor in lower limb amputations. Thus, the loss of touch and proprioception is common, associated not only with discomfort and pain, but also with a decrease in the quality of life. Despite this, diagnostic tools and treatments for the dysfunction of touch and proprioception remain poorly developed, principally because little is known about how these senses work. This knowledge gap reflects a lack of adequate devices for delivering controlled mechanical stimuli and of animal models amenable to analysis of the mechanobiology of touch sensation. The objective of the proposed research is to bridge this gap by developing new devices for controlled force delivery, improved animal models for dissecting force transmission and transduction pathways, and new analytical methods for fundamental study of the relevant mechanics of this basic life process. The proposed research uses the simple roundworm, Caenorhabditis elegans, because more is understood about its sense of touch than that of any other animal. Research using C. elegans has successfully revealed mechanistic aspects of several fundamental and conserved biological processes, including touch sensation. It was in C. elegans, for instance, that the first ion channel proteins required for touch sensation were identified ~20 years ago. Because analogous proteins are expressed in mammalian touch receptor neurons, they may also contribute to touch sensation. At present, C. elegans is the only animal in which we know which proteins form the mechano-electrical transduction channels responsible for detecting force in touch receptor neurons. This knowledge enables a level of analysis that is not currently available in mammalian models. The central hypothesis we are testing is that both force-sensitivity and response dynamics are determined by the interplay of skin mechanics, neuron position, and intracellular, cytoskeletal structures. To test this hypothesis, we will develop new metrics for quantitative assessment of touch sensitivity; new microfabricated tools suitable for delivering pN-5N forces, new in vitro models of touch receptor neurons, and build new models of force transmission and force transduction. The specific aims are: 1) Test the hypothesis that skin mechanics, neuron position, and the neuronal cytoskeleton regulate touch sensitivity in vivo; 2) Assess the impact of body wall muscle tone and internal hydrostatic pressure on touch sensation in vivo; 3) Identify mechanisms of mechano- electrical transduction channel activation and adaptation.